The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Gas hydrates and their formation are significant for the crude oil and natural gas industry. Formed from water and natural gas constituents such as methane, ethane, propane, iso-butane, nitrogen, carbon dioxide and hydrogen sulfide, they pose a great problem, especially when wet gas or multiphase mixtures of water and gas constituents are subjected to low temperatures under high pressure. Under such conditions, gas hydrates can form that lead to blockage of a wide variety of equipment such as pipelines, valves, and other production equipment. The formation of gas hydrates is especially problematic when such multi-phase mixtures are to be transported over relatively long distances at relatively low temperatures such as are found in cold regions of the earth (where the gas mixtures is transported over land) and on the sea bed floor, where production is from sub-sea formations.
One way of preventing the formation of gas hydrate in gas pipelines during transport is to use relatively large amounts—for example more than 10% by weight—of antifreeze alcohol such as methanol or ethylene glycol. These are called thermodynamic inhibitors because they shift the conditions of gas hydrate formation to lower temperatures and higher pressures, so as to inhibit the formation of the hydrates under the conditions being used. On the downside, the use of thermodynamic inhibitors introduces safety concerns such as flash point and toxicity of the inhibitors themselves, along with logistical problems and associated high costs.
As a result of the disadvantages of thermodynamic inhibitors, the industry has made attempts at using other inhibitors in lower amounts (such as less than 2%). The inhibitors either delay gas hydrate formations (kinetic inhibitors) or they keep gas hydrate agglomerates small and therefore pumpable (agglomerate inhibitors or antiagglomerants). Kinetic inhibitors prevent nucleation or growth of gas hydrate particles or modify the growth of the hydrate in such a way that small hydrate particles result.
A wide variety of monomeric and polymeric substances have been identified in patent literature as useful as kinetic inhibitors. Examples include polyvinyl pyrrolidone (WO 94/12761), copolymers of alkoxylated monomers (EP 0896123), polyvinyl alcohol or partially hydrolyzed polyvinyl acetate (EP 1048892) and polyols esterified with fatty acids or alkenyl succinic anhydrides (U.S. Pat. No. 5,244,878). A more recent U.S. Publication No. 2008/0214865 has disclosed polymers made by esterifying pendent hydroxyl groups on the backbone of a polyester polyol and its use of a kinetic hydride inhibitor. Some of these inhibitors have certain drawbacks, such as a lack of biodegradability, and/or the presence of a upper solubility limit in temperature (cloud point). It would be an advance in the art to provide improved kinetic hydrate inhibitors that combine biodegradability and favorable cloud point behavior with effectiveness against hydrate formation at 4 to 6° sub-cooling.